Lubricating oils, heat transfer oils, heat treating oils and electrical discharge machining oils find extensive application in various sectors of industry. Great concern, however, has aroused as these prior art oils tend to get deteriorated upon exposure to heating and oxidizing environments.
The above character of oil is liable to thermally deteriorate with carbonaceous deposits and also with sludge precipitates in some cases because it is often subject to high temperature. Moreover, it oxidatively denatures and deteriorates with the results that acidic material will develop, thus causing metal corrosion and that oxide material will polycondensate, resulting in sludge deposition. In an effort to eliminate the tendency of the oil becoming thermally and oxidatively deteriorative, a number of antioxidants have been proposed which however are all encountered with something poor or defective. No antioxidants are known to have capabilities for all practical purposes.
Deterioration of the foregoing oil will in most instances take place as a result of both heating and oxidizing factors becoming tangled rather than either one of the factors. Those known antioxidants suffer from too low a magnitude of heat resistance to warrant application at elevated temperature.